1. Field of the Invention
The present invention relates to a diaphragm control device incorporated in a lens barrel which includes an automatic diaphragm preset mechanism which retains the diaphragm in a fully open aperture position prior to photography and stops down the diaphragm to a preset aperture value during a camera photographing operation. More particularly, the present invention relates to a diaphragm control device for adjusting the fully open aperture in accordance with a lens adjustment, such as a zooming operation.
2. Description of the Prior Arts
There have already been proposed control devices for adjusting the fully open aperture in a camera in accordance with, for example, a zooming operation, for example, in Japanese published patent specification No. 40-20911, Japanese laid-open-patent specification No. 49-24134, and U.S. Pat. No. 3,889,282. As shown in FIG. 1, however, a typical conventional device comprises an arrangement in which the relative position between motion transmitting members is changed by a correction member which moves along with a component contained in the link system traced from main driving lever 16 (which is biased counter-clockwise by main spring 14) to aperture setting lever 8. In the conventional device, pin 4 follows control lever 2 on a camera body side to rotate aperture setting lever 8 counterclockwise in the diagram to thereby cause fixed pin 8a carried thereby to abut upon aperture control cam 6a so as to determine an angular position of diaphragm operating ring 10 and a diaphragm aperture defined by diaphragm blades 12, i.e., when the control lever 2 moves in the direction of the arrow in response to a camera shutter release operation. Namely, in an example of operation of a device according to FIG. 1, downward extension 8b of aperture setting lever 8 is fitted in correction slot 20b formed in axial extension 20a of intermediate member 20 which is biased clockwise by spring 18, and when aperture setting lever 8 moves in linkage with a zooming operation along the optical axis relative to intermediate member 20, together with diaphragm operating ring 10 and diaphragm blades 12, aperture setting lever 8 rotates relative to intermediate member 20 to thereby adjust the diaphragm aperture.
In such a conventional device, however, the weight of any one of the members in the link system increases by as much as that of the correction member, resulting in an increase in the moment of inertia. Thus, there have arisen the problems as follows:
(I) It becomes difficult to obtain the desired diaphragm dynamic characteristics. (Too much time is required for the diaphragm blades to become stable, for example.)
(II) A large moment of inertia necessitates increased strength of the parts.
(III) The requirements for cam designing for the correction member lessen flexibility in optical designing.
(IV) A solution to the above-described problems results, in all instances in costly designing.